This invention relates to laminar blends of polyolefins and ethylene-vinyl alcohol copolymers which have superior barrier and physical properties.
Polyolefins have been broadly used as packaging materials for foodstuffs and the like because of excellent mechanical strength and sanitariness. However, polyolefins disadvantageously permit high permeability of gases such as oxygen and carbon dioxide. As a result, foodstuffs cannot be preserved for a long time with use of containers or the like formed of polyolefins.
Containers and films which are blends or laminates of polyolefins and ethylene-vinyl alcohol copolymers have been the subject of several investigations because this combination of polymers has the potential for providing high resistance to permeation by water, oxygen and hydrocarbons.
U.S. Pat. No. 3,975,463 discloses a molded structure having a specific multilayer structure and good resistance to gas permeation made from (a) 30 to 98% by weight of a crystalline polyolefin, (b) 2 to 70% by weight of a saponified product of an ethylene vinyl acetate copolymer, and (c) 0.5 to 15 parts by weight of a thermoplastic polymer containing a carbonyl group in the main or side chain. The thermoplastic polymer (c) can be a copolymer of maleic anhydride or an acrylic acid grafted polyethylene.
Prior art laminar articles were found to exhibit significant variation in resistance to permeation by hydrocarbons, water and/or oxygen and in mechanical strength. Such variations are undesirable in laminar structures which are to be used in applications such as containers for hydrocarbon fuels and packaging for perishable foodstuffs. In addition, the components used in laminar articles to be used as containers for foodstuffs often must be approved by the United States Food and Drug Administration or other regulatory authorities. Thus, a need exists to provide polyolefin/ethylene-vinyl alcohol copolymer laminar structures which will consistently provide optimum barrier properties and mechanical strength, and which are approved for use as a container for foodstuffs.